In a related art, there is a sliding door that opens and closes by sliding from side to side in a groove between a door lintel and a doorsill. Such a sliding door only slides straightly in a horizontal direction and when the sliding door is to be placed at the back side or front side of a wall surface, the front surface of the sliding door in the closed position and the wall surface cannot be flat or arranged in the same plane. This causes a problem of bad appearance.
In order to solve this problem, Japanese Patent No. 3686617 discloses a sliding door device having a curved guide rail 32 attached to a part above a sliding door 31 and rollers 33 attached to the sliding door 31 to roll in the guide rail 32, which is illustrated in FIG. 14. With this sliding door device, as the sliding door 31 moves along the curved guide rail 32, the surface of the sliding door 31 in the closed position and the wall surface can be flat and the sliding door 31 in the open position can be arranged on the back side of the wall surface.
Besides, in this sliding door device, there is no guide groove on a floor surface for guiding a lower part of the sliding door. Instead of the groove provided in the floor surface, a sliding door groove 31a is provided in the bottom surface of the sliding door 31, and in the floor surface, a pin body 34 is provided that fits into the sliding door groove 31a in the bottom surface of the sliding door 31. This is because when the guide groove is provided in the floor surface, dust will easily accumulate therein. When the sliding door in the closed position is to be opened, the pin body 34 fits into the sliding door groove 31a. The opening motion of the sliding door 31 is guided by the pin body 34. As it is not preferable that the pin body 34 juts in the opening which people pass through, the pin body 34 is arranged hidden behind the wall surface.    Japanese Patent No. 3686617 (claim 1, FIGS. 1 and 4)